This invention pertains generally to pressure actuated dispensers, applicators and devices for application of fluid materials, and more particularly to an apparatus which is part of a system which allows conventional dispensing devices to be adapted or modified such that a variety of materials in varying quantities may be dispensed from or applied by a single dispensing device.
Various types of dental materials are dispensed from some form of dispensing apparatus (Dragon U.S. Pat. No. 5,061,179). This may facilitate a more ergonomic action or in the case of dental composites, ease of placement. This placement may be enhanced visually by the apparatus or it may be used to overcome a drawback of the material itself. Such is the case with many of the light cured resins currently in use.
To increase strength, micron sized particles are incorporated into the resin such that when the composite is cured in the tooth, it is esthetically satisfactory and will be able to withstand the chewing forces. Today it is common to have filler content over 80%. Delivery of the material is commonly done with a hand actuated dispenser modified to magnify hand pressure as much as 5 times. Such dispensers are coupled with a cartridge filled with the appropriate material for the task. These cartridges usually are friction fit to the proximal end of the dispenser as a convenience factor. The cartridges are mostly uniform in their circumference, however their length may vary. The opening of the distal end contains a plug that when pushed along the longitudinal axis by part of the dispenser expresses the material from the proximal end of the cartridge. Such orifices may vary in size of opening and the length of the cannula that is part of the cartridge may also vary in length.
Owing to the resistance of flow by the very highly filled composites, the orifice of the cartridge can be greater than 3 mm. Multiple handheld devices that magnified the force necessary to overcome the resistance due to viscosity were patented (Kunkel, et al., U.S. Pat. No. 5,871,354). Patents on the size, shape and orifice opening of the cartridge were issued. In each case it was in overcoming the viscosity problem that drove the research. While the industry tried to market these combinations as convenience items, it noted that there was a problem of placing these materials so as not to have voids, incompletely cured resins and uncovered surfaces.
Dental composite materials are mixtures of liquid resins and suspended particles. Light wavelengths of sufficient energy to cause a reaction are introduced to allow the resin to cure producing a sufficiently strong material to withstand the chewing forces of the mouth. Many types of light sources are used but the nature of the material preclude the immediate setting throughout as with a two part chemical set resin system. The initial set starts at the area with the most intense light energy, creating a shrinkage as the material cures to the greatest mass. This occurs regardless of the intensity or wavelength of the light source.
This effect has led to open margins in the first instance which is entirely due to the chemistry of the material. In the second instance, the inability to deliver the material equally to all parts of the preparation, owing to its size, complex shape (angles, undercuts, etc), and location in the mouth are an operator shortcoming. The second instance may be attributed to the viscous nature of the material. The primary obligation of the procedure is to cover the margins such that a completely cured composite material leaves no gaps, voids or uncured material which may lead to recurrent decay.
To facilitate such coverage, reduce the total shrinkage to an acceptable level, and produce a completely cured resin, the manufacturers recommend a layering technique. Operator technique deficiency, owing to the viscous nature of the material, can incorporate voids that will alter the strength and optical properties of the cured material. To overcome the high probability of open margins, the industry introduced a flowable composite with more liquid resins and less filler. This material is placed at the interface of the tooth and retainer (should one be needed) or the floor and sides of the preparation. These flowable composites can be introduced with a cannula as small as 25 ga or smaller.
Again, these flowable composites were initially meant to close margins and reduce the overall shrinkage factor. Operator error is introduced in the use of these materials when bubbles are introduced by the manipulation of the cannula or when too much of the material is introduced into the preparation. More volatile diluents in the resins are incorporated to increase the flow (Klee, et al., U.S. Pat. No. 5,876,210, pps. 13, 14). This action reduces the strength and creates greater shrinkage. There is a decided increase in the vapor pressure that occurs when the material goes from room temperature (approximately 72° F.) to body temperature (98.6° F.), thereby creating tiny bubbles. Any area where there is oxygen present will create an oxygen inhibited layer causing uncured resin that remains uncured.
The overall intent of the manufacturers in their product and its delivery is to wet the surface of the tooth with the resin, primarily to help seal and have a homogeneous material against the tooth surface that will, when cured correctly, produce a restoration of sufficient strength to withstand the chewing forces to prevent breakage.
Patents have been issued that deal with the nature of all viscous materials, dealing with orifice openings, size and shape of the material carrier (cartridge, capsule) (Bender, U.S. Pat. No. 5,707,234), means of multiplying forces necessary to overcome the viscosity and size, shape and mechanical properties of the cartridge holder used to dispense such materials. None have been issued where the resistance to flow caused by the viscosity is overcome by applying controlled heat at the point of delivery (generating heat within the capsule itself). Such heat must be applied within a specific range to take advantage of the optimal flow given to the resin component of the mixture. Such heat range must not in any way alter the chemistry or any of the other desirable properties of the material when in a plastic state or when converted to a cured state.
This invention overcomes all the disadvantages of forcing a viscous material through a small opening by altering the plasticity of a mixture by applying controlled heat allowing a component of the mixture to become fluid.
The advantages to such a method and delivery system include: (1) reduction of voids owing to more consistent placement due to increased flow; (2) greater wetting of the surface of the tooth with the resins in a more liquid state; (3) ease of delivery (a) less force required (b) smaller delivery tips for better visualization; (4) less volatile diluents required, yielding grater strength and less shrinkage; (5) use of longer chain resins for greater strength; (6) ability to incorporate a filler content to 90% and above without compromising the flow using a standard dental hand delivery syringe; (7) the manipulation of the chemistry of the resins such that heating within controlled parameters will deliver the appropriate delta energy to initiate a self-cure; and (8) allow for a two-component system to exist in a premixed state in the same cartridge without setting or degrading prior to intended use until the appropriate delta energy is applied.